INSIDER spoke with the actor behind William — Jimmi Simpson — to learn more about his character's dark twist and what might be in store next.

The first thing Simpson told us was the unexpected way William's fate was accidentally revealed to him early on during filming.

"Well that's kind of a funny story," Simpson said. "Around episode three, I was asked to go to Christian, our makeup designer, so he could look at me. And he was staring at my eyebrows. He said 'Would you mind if I changed your eyebrows?' And I was like no, but as a man no one's ever asked me that question before and so I said, 'What for?' and he started just mumbling because he's not an actor so he's not ready to have a good excuse."

This seemingly insignificant moment set Simpson on the path towards understanding the truth way before the showrunners Jonathan Nolan and Lisa Joy planned on telling him.

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"It was just weird that he didn't give me an answer. I thought about it for awhile and the only conclusion I could come to was that they were trying to make me look like someone else," Simpson said. "When I thought about everyone else the only person I thought it could be was Mr. Harris. And then I just happened to be walking to lunch and Lisa Joy was like 'Hey!' and she started walking with me and I said, 'Christian was just looking at my eyebrows' and I then saw her face — her face got tight, it just tightened. And I said 'Am I ... do I turn into Ed Harris?' and she goes, 'I can't say anything. Don't talk about that!' and I go, 'Okay, okay, okay.' So she kind of confirmed that for me."

Even though Simpson knew himself, he kept the secret close.

"When [Lisa Joy] let me know that it's not to be thought about or talked about, I just took it as law and I didn't discuss it with anybody," Simpson said. "That being said, Evan [Rachel Wood] was kind of the sharpest one of us for calling out what was going to happen. And she brought up that William might be the Man in Black I think around episode four. But then [she] instantly let it go because of the trajectory of William and Dolores. And I know part of it [...] was just wishful thinking on her part, but I also dropped it into my very back pocket."

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The only thing Simpson did differently was observe Ed Harris (the Man in Black) more closely.

"Yes, I paid attention to Ed's stuff but I didn't load the turn into William," he said. "I just watched Ed more. And then towards the end of the season, around episode eight or nine, when William started being affected by these choices [...] I started dropping in a little bit of Mr. Harris' walk and tone."

Though Simpson was carrying the knowledge of William's future with him, Ed Harris remained ignorant of the Man in Black's past. We asked Simpson if he spoke with Harris on set about their two characters at all.

"No," he said. "I don't know if I'm speaking out of turn but my impression and understanding is that Mr. Harris knew last — he was like the last person on set to be like, 'Wait a minute, William's me?' And I mean god d--- he's so brilliant. I rarely was on the same set as him and so when I was, I basically just quietly watched from behind other people. A couple times I said hello to him and explained to him what an icon he is to me, and then when he did find out we crossed paths and he stopped briefly and said, 'You're doing a good job' and he winked at me and that was it."

HBO

Seeing as it took Simpson three episodes (and a clue from the makeup department) to learn the truth, he was shocked to see fans guessing the twist so early on in the season.

"I was really surprised after episode two when people were calling out sh-- — like specific sh-- that you weren't supposed to even think about for four more episodes," he said. "And I was bummed out really briefly because it threatened the idea in my mind that everyone would be shocked and surprised with the narrative. But then with each episode you guys just noticed that sometimes people figured out some of the devices that were happening but it never seemed to affect the emotional unfolding of the story or even just the peaks and the valleys. The theories and the fan boys didn't take away any of the enjoyment as a whole."

We asked Simpson about his feelings regarding William's path towards the Man in Black's more warped sense of the park.

"Because I didn't have the information on why when I understood that I was turning into him, I didn't judge it or really think about it yet," Simpson said. "And then once it became clear that the reason this occurs is the man falls deeper in love than he ever had and his heart is shattered, I can relate to that."

For Simpson, the emotional aspect of William's journey was an anchoring point and made him a more complex and realistic "villain."

HBO

"Lucky enough I'm a funny-looking guy and I've played a hell of a lot of creepy characters in my life, and I don't tend to judge these humans because I do need to play an emotional, true self," he said. "I've never been able to just say 'Oh well this guy's a bad guy' [...] it's more like, 'What could this person be thinking to have them do this?' and often the answer is a deep love for another human."

According to Simpson, William's love for Dolores wound up being a wound that couldn't be healed.

"With William, I mean god d--- did he fall in love with Dolores," Simpson said. "And to realize after he makes that choice, that he's gonna do what he needs to do and compromise all these values he had to get this girl — and then that's not even enough — he realizes well sh-- I'm free and I'm capable of anything and I think what I'm going to do is run this whole place. And so he didn't just do it because he wants to be a god, he did it because a girl broke his heart and he's trying to recover."

William's final scenes in episode ten showed the present day Man in Black confronted with an army of sentient hosts shooting at him. His fate is unclear, and it's also unclear if we'll see Simpson back in his role. Season two may not have a need for the flashbacks to his character's origin story anymore. We asked Simpson if he could tell us anything about what's in store.

"Well, I haven't been told anything," he said. "I think they're keeping the lid pretty tight but I did hear 'Holy sh-- season two is going to be so cool' from one of the writers. So that could be anything but I wouldn't doubt it because [Jonathan Nolan and Lisa Joy] are like … oh my god. I think we've only seen the tip of the iceberg from these guys."